24 ANIMAL FORMS 
to assign such forms to a definite position among the 
sponges. 
26. Structure of a simple sponge.—In the simpler sponges 
the body is usually vase-shaped (Fig. 13), with the base 
fastened to some foreign 
object, while at an oppo- 
site end an opening leads 
b ‘A into a comparatively large 
4a internal cavity. This lat- 
ter space is also put in 
communication with the 
exterior by a multitude of 
minute pores which pene- 
trate the body wall. In 
Fic. 12.—Various forms of sponges, natural size. (From Nature.) 
the living condition currents of water continually pass 
through these smaller canals, and out of the large termi- 
nal opening, thus bringing within reach of the body minute 
